Electromagnetic counterparts of compact object mergers powered by the radioactive decay of r‐process nuclei

By B. Metzger, G. Mart'inez-Pinedo, S. Darbha, E. Quataert, A. Arcones, D. Kasen, R. Thomas, P. Nugent, I. Panov, Nikolaj Thomas Zinner. 2010

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The most promising astrophysical sources of kHz gravitational waves (GWs) are the inspiral and merger of binary neutron star(NS)/black hole systems. Maximizing the scientific return of a GW detection will require identifying a coincident electromagnetic (EM) counterpart. One of the most likely sources of isotropic EM emission from compact object mergers is a supernova-like transient powered by the radioactive decay of heavy elements synthesized in ejecta from the merger. We present the first calculations of the optical transients from compact object mergers that self-consistently determine the radioactive heating by means of a nuclear reaction network; using this heating rate, we model the light curve with a one-dimensional Monte Carlo radiation transfer calculation. For an ejecta mass ~ 10 -2 M ⊙ (10 -3 M ⊙ ) the resulting light-curve peaks on a time-scale ~1 d at a V-band luminosity vL v ~ 3 x 10 41 (10 41 )erg s -1 [M V = -15(-14)]; this corresponds to an effective 'f' parameter ~3 × 10- 6 in the Li-Paczynski toy model. We argue that these results are relatively insensitive to uncertainties in the relevant nuclear physics and to the precise early-time dynamics and ejecta composition. Since NS merger transients peak at a luminosity that is a factor of ~10 3 higher than a typical nova, we propose naming these events 'kilo-novae'. Because of the rapid evolution and low luminosity of NS merger transients, EM counterpart searches triggered by GW detections will require close collaboration between the GW and astronomical communities. NS merger transients may also be detectable following a short-duration gamma-ray burst or 'blindly' with present or upcoming optical transient surveys. Because the emission produced by NS merger ejecta is powered by the formation of rare r-process elements, current optical transient surveys can directly constrain the unknown origin of the heaviest elements in the Universe.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/f86a0b023e1e0924059824aa674c40d8d111e03b

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Citations in the corpus

GLADE: A galaxy catalogue for multimessenger searches in the advanced gravitational-wave detector era (2018, background): “Binary neutron star (BNS) coalescences followed by possible kilonova emissions (see e.g. Li & Paczyński 1998, Metzger et al. 2010, Tanvir et al. 2013) are currently the most promising sources for joint GW and EM observations.”
Production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers (2016, background): “…due to the realization that the radioactive decay of the r-process ejecta can power a thermal transient (a “kilonova”; e.g., Li & Paczyński 1998, Metzger et al. 2010, Roberts et al. 2011, Barnes & Kasen 2013, Tanaka & Hotokezaka 2013), which could serve as a promising electromagnetic…”
MASTER Optical Detection of the First LIGO/Virgo Neutron Star Binary Merger GW170817 (2017, background): “The possibility of a kilonova explosion resulting from the decay of radioactive elements in the expanding envelope was discussed in Li & Paczynski (1998), Freiburghaus et al. (1999), Rosswog et al. (1999), Rosswog (2005), Metzger et al. (2010), and Coughlin et al. (2017).”
Delayed outflows from black hole accretion tori following neutron star binary coalescence (2013, background): “…et al. 2011; East et al. 2012; Rosswog 2012; Rosswog et al. 2013; Bauswein et al. 2013), and recent nuclear reaction network calculations largely agree on the amount of radioactive heating provided by such decaying r-process elements (Metzger et al. 2010; Roberts et al. 2011; Goriely et al. 2011).”
FERMI GBM OBSERVATIONS OF LIGO GRAVITATIONAL-WAVE EVENT GW150914 (2016, background): “suggested, notably r-process transients produced in the ejecta resulting from the binary merger (Metzger et al. 2010), only one such event has been reported (Tanvir et al.”
Formation of Double Neutron Star Systems (2017, background): “These short GRBs (sGRBs) are possibly followed by a socalled “kilonova” or “macronova” (Li & Paczyński 1998; Kulkarni 2005; Metzger et al. 2010; Barnes & Kasen 2013; Tanaka & Hotokezaka 2013; Tanvir et al. 2013; Berger et al. 2013; Fernández & Metzger 2015; Metzger 2016; Gottlieb et al. 2017).”
WHAT IS THE MOST PROMISING ELECTROMAGNETIC COUNTERPART OF A NEUTRON STAR BINARY MERGER? (2011, methodology): “…of this association, the mergers are expected to be accompanied by isotropic thermal emission, powered by the radioactive decay of heavy elements in the merger ejecta (Li & Paczyński 1998; hereafter LP98; Kulkarni 2005; Rosswog 2005; Metzger et al. 2010; Roberts et al. 2011; Goriely et al. 2011).”
Three-dimensional GRMHD Simulations of Neutrino-cooled Accretion Disks from Neutron Star Mergers (2017, methodology): “Though not included in our simulations, the outflows will receive additional nuclear heating from the r-process on larger radial scales of ≈ 2−3 MeV per nucleon (Metzger et al. 2010a), which will boost its speed by an additional ≈ 10 − 20%.”
r-PROCESS LANTHANIDE PRODUCTION AND HEATING RATES IN KILONOVAE (2015, background): “Additionally, radioactive decay of unstable nuclides formed during decompression of the ejecta can power a transient in the optical or infrared that peaks on a timescale of a day to a week (Li & Paczyński 1998; Kulkarni 2005; Metzger et al. 2010; Kasen et al. 2013; Tanaka & Hotokezaka 2013).”
The long-term evolution of neutron star merger remnants – I. The impact of r-process nucleosynthesis (2013, background): “Metzger et al. (2010) argue that this fraction must be th ≈ 0.25...1.”
EFFECT OF A HIGH OPACITY ON THE LIGHT CURVES OF RADIOACTIVELY POWERED TRANSIENTS FROM COMPACT OBJECT MERGERS (2013, methodology): “More recent, more detailed, models (Metzger et al. 2010; Roberts et al. 2011) have used nuclear reaction networks to determine the radioactive heating rate and Monte Carlo radiation transport to calculate merger light curves, under the assumption that the opacities of heavy r -process elements…”
RADIATIVE TRANSFER SIMULATIONS OF NEUTRON STAR MERGER EJECTA (2013, methodology): “Following the methods of Metzger et al. (2010) and Korobkin et al. (2012), we introduce the efficiency of thermalization therm for the β decay energy.”
r-PROCESS NUCLEOSYNTHESIS IN DYNAMICALLY EJECTED MATTER OF NEUTRON STAR MERGERS (2011, methodology): “This must be expected to lead to significant differences in the brightness evolution of the kilo-nova because its peak bolometric luminosity scales with Lpeak ∝ v1/2expM1/2ej and, for free expansion (vexp = const), is reached on a time-scale tpeak ∝ v−1/2exp M1/2ej (Metzger et al. 2010; Arnett 1982)”
Multi-messenger observations of a binary neutron star merger (2017, methodology): “…(i) early optical and infrared emission, a so-called kilonova/macronova (hereafter kilonova; Li & Paczyński 1998; Kulkarni 2005; Rosswog 2005; Metzger et al. 2010; Roberts et al. 2011; Barnes & Kasen 2013; Kasen et al. 2013; Tanaka & Hotokezaka 2013; Grossman et al. 2014; Barnes et al. 2016;…”
OPACITIES AND SPECTRA OF THE r-PROCESS EJECTA FROM NEUTRON STAR MERGERS (2013, background): “For r-process ejecta at 1 day, Metzger et al. (2010) find ̇ ≈ 1 eV s−1 Considering values ∆E ∼ 1 eV, T ≈ 5000 K and f ∼ 1/3, the ratio Rnt/Rbb ≈ 10−8.”